Slab furnace with restricted enclosing chamber



J. F. R. JONES 3,356,355 SLAB FURNACE WITH RESTRICTED ENCLOSING CHAMBER Dec. 5, 1967 Filed Jan. 18, 1965' INVENTOR B Y lfuwba @2002;

United States Patent Ofiice 3,356,355 SLAB FURNACE WITH RESTRICTED ENCLOSING CHAMBER John F. R. Jones, Neston, England, assignor of one-third to John Summers & Sons Limited, Shotton, and onethird to Stein Atkinson Stordy Limited, Richmond, England, both British companies Filed Jan. 18, 1965, Ser. No. 426,120 Claims priority, application Great Britain, Jan. 20, 1964, 2,410/ 64 3 Claims. (Cl. 266-24) ABSTRACT OF THE DISCLOSURE This invention relates to a slab furnace having a hearth along which slabs are passed, the hearth being located in an enclosing chamber and being provided with side walls which extend above and preferably below the level of the slabs and in which means are provided for balancing the pressures of gases above and below the hearth so that gases do not flow between the upper and lower parts of the chamber around the edges of the slabs.

This invention relates to slab furnaces of the type (hereinafter referred to as the type specified) comprising a hearth through which slabs to be heat treated may be located with the leading and trailing edges of successive slabs substantially joining and a number of fixing zones disposed at spaced locations along the length of the furnace and below the hearth.

Such furnaces are well known, are usually top as well as bottom fired and are generally operated continuously for the heat treatment of steel slabs to be fed to a rolling mill. The slabs pass through the hearth supported upon skid rails with their end edges spaced from the side walls of the hearth the latter in turn being spaced inwardly from the side walls of the furnace to provide passages for exhaust gases communicating with exhaust openings located at the charging end of the furnace.

In previously known constructions combustion gases from above the slabs generally pass into the passages in a direction nearly parallel with the upper surfaces of the slabs whereas since the skid rails supporting the slabs are usually themselves supported upon spaced pillars cornbustion gases from below the slabs generally leave the hearth in a direction normal to the lower surfaces of the slabs.

In addition as the products of combustion pass from each firing zone towards the charge end of the furnace considerable transfer takes place around the end edges of the slabs from the lower to the upper part of the hearth.

The two flow characteristics referred to above have the effect of overheating the upper surfaces of the slabs and additionally overheating their end edges compared with their central portions.

It is an object of the present invention to provide an improved furnace of the type specified which permits slabs to be heat treated so that all parts of each slab achieve substantially the same temperature.

According to one aspect of the present invention there is provided a slab furnace of the type specified comprising a hearth having side walls extending sufficiently above the level at which slabs are supported therein to ensure that the initial movement of combustion gases from above the slabs is in a direction substantially normal to the upper surface thereof and comprising means for maintaining the combustion gas in the upper part of the hearth above the slabs at substantially the same pressure as the combustion gas in the lower part of the hearth below the slabs so as substantially to preclude gas flow between said lower and upper parts around the end edges of the slabs. Prefer- 3,356,355 Patented Dec. 5, 1967 ably said means comprises a constriction in the exhaust gas path from the upper part of the hearth. The constriction may be an inwardly turned lip at the upper end of each of the side walls of the hearth. Advantageously a second smaller inwardly turned lip is provided at the lower end of each of the side walls of the hearth.

One embodiment of the invention will now be described by way of example with reference to the single figure of the accompanying drawing which shows a transverse section through a continuous slab furnace illustrating diagrammatically the general flow pattern of the combustion gases.

Referring to the drawing the furnace comprises a base 1 side walls 2 and 3 a roof 4 and an end wall 5 at the charge end of the furnace. Two discharge openings 6 and 7 for exhaust combustion gases are provided in the lower corners of the end wall 5 and the furnace comprises a central hearth indicated generally at 8 extending along its entire length. The hearth has a floor 9 and side walls 10 and 11 respectively spaced from the furnace walls 2 and 3 to provide passages 12 and 13 respectively communicating with the openings 6 and 7. The floor 9 of the hearth is raised above the level of the base 1 and is formed with openings 14 communicating with an interconnected series of tunnels 15 which also communicate with both the passages 12 and 13.

A series of spaced apart pillars 16 extend upwardly from the floor 9 of the hearth 8 to support longitudinally extending skid rail structures 17 on which steel slabs 18 may be passed continuously from the charge end of the furnace to its discharge end. As shown the end edges 19 of the slab 18 are spaced from the side walls of the hearth and it will be understood that the leading and trailing edges of each slab respectively adjoin the edge of the next slab.

The lower parts of the walls 10 and 11 at the position of the transverse tunnels 15 are formed with inwardly turned lips 20 and the upper ends of these walls are formed with inwardly turned lips 21 which extend inwardly of the walls a greater distance than the walls 20.

It will also be understood that at intervals along the length of the furnace firing zones are provided both above and below the hearth 8.

The walls 10 and 11 extend sufficiently above the level of the slabs 18 to provide the hearth 3 with a partially enclosed upper part 22 having a central discharge opening 23 for combustion gases between the lips 21. Thus combustion gases from the upper part of the hearth initially travel from the slabs 18 in a substantially vertical direction normal to the upper surface of the slabs. This ensures that the passages of these combustion gases away from the upper surface of the slabs does not tend to heat the end edges 19 of the slabs to a temperature higher than the remainder thereof.

In addition it will be appreciated that there is a tendency for combustion gases from the lower part of the hearth below the slabs 18 to pass upwardly between the end edges 19 of the slabs and the walls 10 and 11 into the upper part 22 of the hearth. This tendency is substantially obviated by the provision of the restricted opening 23 for the exhaust of combustion gases from the part 22. The size of this opening is arranged in relation to the size of the slabs 18 (i.e. the spacing of the latter from the walls 10 and 11) the size of the apertures 14 and the disposition and heat output of the firing zones so that in operation a higher pressure exists in the upper par-t 22 of the hearth than would otherwise exist so as just to balance the buoyancy of the hot combustion gases beneath the slabs 18 and prevent any substantial gas flow around the end edges 19 thereof.

The general flow pattern of the combustion gases in the upper and lower portions of the hearth in relation to the slabs 18 and edges 19 thereof, as described above, is illustrated diagrammatically by the direction arrows on the drawing.

It will be appreciated that although it is convenient to provide the constriction in the form of lips 21 to the walls of the hearth 8 such constriction could be provided in the passages 12 and 13.

I claim:

1. A slab furnace comprising an enclosing chamber defining a discharge opening for exhaustion of combustion gases, a hearth within the chamber having a floor over which slabs to be treated are passed with the leading and trailing edges of successive slabs substantially joining, a number of firing zones disposed at spaced locations along the length of the furnace above and below the hearth, the hearth and the chamber defining a space below the slabs which space is connected to the discharge opening, the hearth having side walls spaced from the chamber walls and extending above the level at which the slabs are supported and defining between them a space above the slabs, the walls further defining an opening forming part of a flow passage connecting the space above the slabs with the discharge opening, and a constriction in the flow passage so dimensioned that under optimum firing conditions the pressures of gases above and below the slabs is balanced to prevent flow of gases around the edges thereof.

2. A slab furnace according to claim 1 in which the constriction is an inwardly turned lip at the upper end of each of the side walls of the hearth.

3. A slab furnace according to claim 2 in which each of the side walls of the hearth extend below the level of the slabs and a second smaller inwardly turned lip is provided at the lower end of each of the side walls of the hearth.

References Cited UNITED STATES PATENTS 1,421,155 6/1922 Booth 25142 1,815,890 7/1931 Brockway 26327 1,851,717 3/1932 Meehan 266-5 X 2,974,387 3/1961 Tomkins 25--l42 I. SPENCER OVERHOLSER, Primary Examiner.

E. MAR, Assistant Examiner. 

1. A SLAB FURNACE COMPRISING AN ENCLOSING CHAMBER DEFINING A DISCHARGE OPENING FOR EXHAUSTION OF COMBUSTION GASES, A HEARTH WITHIN THE CHAMBER HAVING A FLOOR OVER WHICH SLABS TO BE TREATED ARE PASSED WITH THE LEADING AND TRAILING EDGES OF SUCCESSIVE SLABS SUBSTANTIALLY JOINING, A NUMBER OF FIRING ZONES DISPOSED AT SPACED LOCATIONS ALONG THE LENGTH OF THE FURNACE ABOVE AND BELOW THE HEARTH, THE HEARTH AND THE CHAMBER DEFINING A SPACE BELOW THE SLABS WHICH SPACE IS CONNECTED TO THE DISCHARGE OPENING, THE HEARTH HAVING SIDE WALLS SPACED FROM THE CHAMBER WALLS AND EXTENDING ABOVE THE LEVEL AT WHICH THE SLABS ARE SUPPORTED AND DEFINING BETWEEN THEM A SPACE ABOVE THE SLABS, THE WALLS FURTHER DEFINING AN OPENING FORMING PART OF A FLOW PASSAGE CONNECTING THE SPACE ABOVE THE SLABS WITH THE DISCHARGE OPENING, AND A CONSTRUCTION IN THE FLOW PASSAGE SO DIMENSIONED THAT UNDER OPTIMUM FIRING CONDITIONS THE PRESSURES OF GASES ABOVE THE BELOW THE SLABS IS BALANCED TO PREVENT FLOW OF GASES AROUND THE EDGES THEREOF. 